This tells the markdown code that the following block is SQL and it will colour the text accordingly. To wit:

select*fromtablewherenamelike'Volker%'orderbyidasc;

Note how SQL keywords (not all SQL Anywhere keywords - TODO) are coloured. Without the ":::SQL" it just shows up like this:

select * from table where name like 'Volker%' order by id asc;

If you don't have a language indicator, the markdown code attempts to determine what language it is, but I've found usually gets it wrong. In the preview window, you do not see the syntax colouring but in the final result, it should show up - and the ":::SQL" line should vanish.

You can use a whole bunch of language indicators: ":::bash" for shell scripts, ":::C", ":::C++", ":::python", ":::perl", etc.

There's some weirdness with lists. There was no way for markdown to detect the end of the list so it tried to include the code block in the list element and did not format it as a code block. The "solution" was to end the list and add a separate paragraph after the end of the list.